This invention generally pertains to control devices. More specifically, the present invention relates to a control device which senses an abnormal condition and shuts down a heating device as a result thereof.
The invention is particularly applicable to a humidifying tower of a corrosion testing device and will be described with particular reference thereto. However, it will be appreciated by those skilled in the art that the invention has broader applications and may also be adapted for use in other types of devices.
Corrosion testing is required of many items which must meet corrosion resistance standards set by various governmental agencies and industrial concerns. The testing of the ability of various products to withstand corrosive influences such as salt vapor is frequently conducted by accelerated exposure techniques. These methods utilize a test cabinet into which parts to be tested are placed. A corrosive atmosphere, for example, salt vapor fog is introduced into the cabinet in specified amounts for specified periods of time. Exposed items are then removed from the cabinet and scrutinized for signs of corrosion, structural breakdown, and the like.
Generally, corrosion testing devices are compact, approximately the size of a home food freezer. Since there is not a great deal of excess space within the corrosion testing cabinet, feed mechanisms for feeding the corrosive gases and liquids to appropriate outlets on the cabinet are provided on the outside of the cabinet. Necessary adjuncts to the cabinet are an air saturation tower, a salt solution reservoir and two storage tanks to supply the liquid to the tower and reservoir.
The air saturation or "bubble" tower functions to give air introduced into the cabinet a uniform humidity. To accomplish this result, air is bubbled into the bottom of the saturation tower and passes through water to acquire the desired humidity. Saturated air is then drawn from the top of the tower and is introduced into an atomizing nozzle of a fog tower in the cabinet. A certain amount of water in the air saturation tower is evaporated by the air passing therethrough with the result that the level of the water within the tower is lowered. It is therefore necessary that a replenishing supply be connected to the tower to replenish the water therein.
Generally, a heater is provided in the bottom of the tower to heat the liquid contained therein. A temperature control is electrically connected to the heater to maintain the desired operating temperature in the tower. However, if the temperature control malfunctions raising the temperature of the tower or if for some reason such as a leaky water delivery line, an empty water reservoir, or operator neglect, the water level in the tower should be insufficient, the tower, which is generally made from a transparent plastic material for easy visual inspection, may be damaged due to heating. In other words, the tower may possibly melt due to overheating and the remaining contents thereof leak out onto the floor.
Accordingly, it has been considered desirable to develop a new and improved control device for corrosion testing apparatus which would overcome the foregoing difficulties and others while providing better and more advantageous overall results.